The present invention relates to novel stabilizers of radiopharmaceutical compositions used for diagnosis and therapy. In particular, the invention relates to use of a hydrophilic thioether, to increase the shelf-life of diagnostic and therapeutic radiopharmaceuticals.
A number of radionuclides are routinely employed in nuclear medicine, both as diagnostic agents and as therapeutics. For example, 99mTc, 111In, 18F, and 201Tl are employed as diagnostic imaging agents, and 131I, 32P, 89Sr, and 153Sm are in therapeutic use. In addition, nuclides such as 186Re, 188Re, 212Bi, 213Bi, 90Y, 67Cu, 192Ir, 165Dy, and 117mSn have been proposed as potential therapeutic agents. Such radionuclides are administered in the form of radiopharmaceutical compositions, which generally include a chelator for the nuclide. Radiopharmaceuticals may additionally include a targeting molecule such as a monoclonal antibody, an antibody fragment, or a receptor ligand. The availability of radiopharmaceuticals has significantly advanced diagnosis and treatment of a variety of diseases.
Chemical decomposition may limit a radiopharmaceutical's shelf life by decreasing the radiochemical purity of the agent over time. For example, a radiopharmaceutical containing 99mTc, 186Re, or 188Re may be susceptible to oxidation of the nuclide itself. In addition, the radiation emitted from a radionuclide can break chemical bonds of other components of the composition, thus causing autoradiolysis. Autoradiolysis is a particular problem when the radiopharmaceutical contains higher energy nuclides, such as β-emitters (e.g., 186Re, 188Re, 90Y, 131I) and α-emitters (e.g., 213Bi, 212Bi, 211At, 225Ac, 223Ra).
Thus many radiopharmaceuticals require stabilizers to maximize shelf life. Such stabilizers must be non-toxic and must be able to maintain the product's radiochemical purity for an acceptable shelf-life as well as during use. In addition, an acceptable radiopharmaceutical stabilizer must not interfere with delivery of the radionuclide to the target site.
Methods for stabilizing radiopharmaceuticals by adding gentisates are disclosed, for example, in U.S. Pat. Nos. 4,232,000; 4,233,284; 4,497,744; 5,384,113. Stabilization of radiopharmaceuticals using ascorbic acid is disclosed in U.S. Pat. Nos. 5,393,512 and 5,011,676, in WO 97/28181 and in WO 98/33531. Hydroquinone stabilizers of radiopharmaceuticals is disclosed in U.S. Pat. No. 4,229,427. Other compounds such as reductic acid, erythorbic acid, p-aminobenzoic acid, 4-hydroxybenzoic acid, nicotinic acid, nicotinamide, 2,5-dihydroxy-1,4-benzenedisulfonic acid, tartaric acid, inositol, and the like, have also been used to stabilize radiopharmaceutical compositions.
U.S. Pat. No. 5,384,113 discloses a method of preventing autoradiolysis of peptides radiolabeled with 111In using gentisic acid or gentisyl alcohol. In addition to preventing autoradiolysis of peptides by 111In, the method of U.S. Pat. No. 5,384,113 is proposed to prevent autoradiolysis of peptides by 67Ga, 169Yb, 125I, 123I, and 201Tl. Two radiolabelled peptides, 111In-DTPA-octreotide and 123I-LHRH, were tested for autoradiolysis prevention. A monoclonal antibody, NR-Lu-10, labeled with 186Re was also specifically exemplified.
As indicated in Example 1, infra, the present inventors have found that that when added as a component in radiopharmaceutical kit formulations, gentisic acid decreases the radiochemical purity of some 99mTc-labelled peptides, and thus is not useful as a stabilizer of some radiolabeled peptides. A need exists, therefore, for additional stabilizers of radiopharmaceuticals. A particular need exists for stabilizers of radiopharmaceuticals containing less than 70 amino acids linked by peptide bonds.
Methionine residues in proteins and polypeptides are known to oxidize to methionine sulfoxide. U.S. Pat. No. 5,272,135 discloses a method of inhibiting oxidation of a liquid or semi-liquid composition of a polypeptide containing at least one methionine residue by adding between 0.01% w/v to 0.3% w/v methionine to the composition. U.S. Pat. No. 5,272,135 teaches that the method disclosed therein is effective with a variety of polypeptides, including epidermal growth factor, insulin-like growth factor I, nerve growth factor, transforming growth factor alpha precursor, transforming growth factor beta precursor, transforming growth factor beta, fibroblast growth factor, vaccinia growth factor, platelet derived growth factor, or methionine containing biologically active fragments or precursors of such growth factors. However, the data presented in U.S. Pat. No. 5,272,135 are limited to addition of methionine to inhibit oxidation of methionine residues present in epidermal growth factor. Lam, et al. (1997) J. Pharm. Sci. 86, 1250-1255 disclose the use of methionine to stabilize the recombinant humanized monoclonal antibody rhuMAb HER2 in liquid formulations to prevent oxidation of methionine residues.
U.S. Pat. No. 5,358,708 discloses a method for increasing the storage stability of an aqueous formulation of granulocyte-macrophage colony stimulating factor or an interleukin by addition of a stabilizing amount of methionine, histidine, or mixtures thereof. U.S. Pat. No. 5,358,708 also discloses that chemical differences among proteins causes different proteins to become inactivated during storage at different rates and under different conditions. U.S. Pat. No. 5,358,708 further discloses that the storage-prolonging effects of methionine and histidine are not equivalent with different proteins, and that mixtures of amino acids exhibit different effects as the ratio varies, as the identity of the protein is changed, and/or as concentrations are altered.
WO 97/14430 discloses use of hydrophilic thioethers as antioxidants to prolong storage stability of aqueous formulations of proteins and peptides. The only data presented in WO 97/14430 relate to insulin-like growth factor I, a 70-amino acid peptide containing three disulfide bonds. WO 97/14430 further discloses that common antioxidants such as ascorbic acid, sodium thiosulfate, glutathione, or sodium bisulfite increased oxidation of IGF-1 or even precipitated the protein.